The present invention relates to an extraction device employing an endless screw driven in a sweeping movement over an angular path of 360.degree. and covering the circular floor of a silo containing matter in bulk, for example granulous or pulverulent matter.
Numerous devices incorporating an Archimedean screw are known, adapted to angularly sweep over the circular floor of a silo and bringing to the centre thereof the matter taken along by the screw, said matter being evacuated at the centre through an opening, for example an evacuation funnel, towards a take-up member, for example a conveyor positioned at a level lower than the floor of the silo.
The motor for driving the endless screw is conventionally positioned plumb with the evacuation funnel and is protected by an upper protective cone on which the bulk matter lies.
Devices of this encounter the problem of finding the fulcra necessary for the motorized end of the endless screw, it being observed that the screw must be able to cover an angle of 360.degree. so as to serve the whole of the circular floor of the silo.
Furthermore, it is also necessary to respect the maximum of free section for the passage of the matter at the evacuation opening for example at the (inverted) base of the evacuation funnel.
According to French Pat. No. 71 38336, the screw and motor system is suspended from the centre of a diametrical beam passing through the whole of the silo and of which the upturned V section protects the screw and its motor and the regular flow of the product contained in the silo. Furthermore, this system allows convenient access to the motor whilst completely freeing the section of passage of the evacuation funnel; however, this device, which had given satisfaction, is no longer suitable for large-dimensioned silos responding to present-day needs and of which the diameter, and consequently the span of the diametrical beam, exceeds ten meters, bringing about bending stresses and an excessive camber.